This application is based on and incorporates herein by reference Japanese Patent Application No. 2002-54404 filed on Feb. 28, 2002.
The present invention relates to a semiconductor magnetic sensor that measures the magnitude of a magnetic field.
Such a semiconductor magnetic sensor is disclosed in, for example, xe2x80x9cA High-Resolution Integrated Magnetic Sensor Using Chopper-Stabilized Amplification,xe2x80x9d (Technical Digest of the 12th Sensor Symposium, 1994, pages 205-208).
As shown in FIG. 1A, the semiconductor magnetic sensor 6 of the publication has an n channel MOSFET structure. The sensor 6 includes a p-type semiconductor substrate 5, a source 1, a drain 2, a gate insulating film 4, and a gate 3. The source 1 is located in a surface of the substrate 5 and further includes a first n+ source region 1a and a second n+ source region 1b. The drain 2 is also located in the surface of the substrate 5 and further includes a first n+ drain region 2a and a second n+ drain region 2b. The gate insulating film 4 is made of, for example, silicon oxide and located on the surface of the substrate 5 between the source 1 and the drain 2. A channel region 9, where a channel is induced for electrically connecting the source 1 and the drain 2, is located between the source 1 and the drain 2 at the surface of the p-type semiconductor substrate 5.
As shown in FIG. 1B, a constant current circuit 7 supplies constant currents of same magnitudes to the two n+ drain regions 2a, 2b using wiring lines that are electrically connected to the drain regions 2a, 2b through two drain contact holes. The currents flowing through the n+ source regions 1a, 1b respectively flow into two wiring lines that are electrically connected to the source regions 1a, 1b through two source contact holes. The currents flowing in the wiring lines connected to the source regions 1a, 1b are measured using current sensors 8. The difference between the currents is calculated. The magnitude of a magnetic field where the sensor is placed is measured on the basis of the difference between the currents, which is generated according to the following mechanism.
When the sensor 6 is not in a magnetic field, the number of the carriers that flow per unit time from the first source area 1a to the first drain area 2a is substantially equal to that from the second source area 1b to the second drain area 2b. However, when the sensor 6 is placed in a magnetic field that is orthogonal to the surface of the substrate 5, the carriers that flow through the channel, which is induced in the channel region 9 using the gate 3, are deflected due to the Lorentz force. As a result, for example, some of the carriers flow from the second source region 1b into the first drain region 2a, as shown in FIG. 1C. Therefore, the difference between the currents is generated. In other words, in the sensor 6, the difference between the currents is generated due to the Hall effect.
However, in the sensor 6, the carriers that flow in the median area of the carrier current mainly contribute to the difference between the currents. Therefore, the difference between the currents is relatively small, and the sensitivity of the sensor 6 of the publication is not satisfactory enough.
The present invention has been made in view of the above aspects with an object to enhance the sensitivity of a semiconductor magnetic sensor by increasing the difference between the currents that vary in response to the magnitude of a magnetic field where the sensor is placed.
To achieve the above object, a semiconductor magnetic sensor according to the present invention includes a semiconductor substrate, a source, a drain, a gate, and a carrier condensing means. The source and the drain are located in a surface of the substrate. One of the source and the drain includes adjoining two regions. The gate is located between the source and the drain for drawing minority carriers of the substrate to induce a channel, through which the carriers flow between the source and the drain to form a channel carrier current. The carriers flow out of the channel into the two regions to form two regional carrier currents. The magnitude of a magnetic field where the sensor is placed is measured using the difference in quantity between the two regional carrier currents. The carrier condensing means locally increases carrier density in the channel carrier current in the proximity of an axis that passes between the two regions in order to increase the difference in quantity between the two regional carrier currents.